Laser welding transparent glass sheets using low melting glass or thin absorbing films

ABSTRACT

A method of sealing a workpiece comprising forming an inorganic film over a surface of a first substrate, arranging a workpiece to be protected between the first substrate and a second substrate wherein the inorganic film is in contact with the second substrate; and sealing the workpiece between the first and second substrates as a function of the composition of impurities in the first or second substrates and as a function of the composition of the inorganic film by locally heating the inorganic film with a predetermined laser radiation wavelength. The inorganic film, the first substrate, or the second substrate can be transmissive at approximately 420 nm to approximately 750 nm.

CROSS REFERENCES

The instant application is co-pending with and is a continuation of U.S.application Ser. No. 15/066,704, filed Mar. 10, 2016 which is acontinuation-in-part of U.S. Pat. No. 9,515,286 granted Dec. 6, 2016which claims the priority benefit of U.S. Provisional Application No.61/822,048, filed May 10, 2013 and entitled, “Laser Welding TransparentGlass Sheet Using Low Melting Glass Film,” U.S. Provisional ApplicationNo. 61/886,928, filed Oct. 4, 2013 and entitled “Laser WeldingTransparent Glass Sheets Using Ultraviolet Absorbing Film,” and U.S.Provisional Application No. 61/829,379, filed May 31, 2013 and entitled“Laser Sealing Using Low Melting Temperature Glass for HermeticDevices,” the entirety of each being incorporated herein by reference.The instant application is co-pending with and is a continuation of U.S.application Ser. No. 15/090,978, filed Apr. 5, 2016 which is acontinuation of U.S. Pat. No. 9,515,286 granted Dec. 6, 2016 whichclaims the priority benefit of U.S. Provisional Application No.61/822,048, filed May 10, 2013 and entitled, “Laser Welding TransparentGlass Sheet Using Low Melting Glass Film,” U.S. Provisional ApplicationNo. 61/886,928, filed Oct. 4, 2013 and entitled “Laser WeldingTransparent Glass Sheets Using Ultraviolet Absorbing Film,” and U.S.Provisional Application No. 61/829,379, filed May 31, 2013 and entitled“Laser Sealing Using Low Melting Temperature Glass for HermeticDevices,” the entirety of each being incorporated herein by reference.

BACKGROUND

Many modern devices require hermetic environments to operate and manyamongst these are “active” devices which require electrical biasing.Displays such as organic light emitting diodes (OLED) that require lighttransparency and biasing are demanding applications due to their needfor absolute hermeticity as a result of the use of electron-injectionmaterials. These materials would generally decompose at atmospherewithin seconds otherwise, so the respective device should maintainvacuum or inert atmospheres for long periods of time. Furthermore, thehermetic sealing should be performed near ambient temperatures due tohigh temperature sensitivity of the organic material to be encapsulated.

Frit-based sealants, for instance, include glass materials ground to aparticle size ranging typically from about 2 to 150 microns. Forfit-sealing applications, the glass frit material is typically mixedwith a negative CTE material having a similar particle size, and theresulting mixture is blended into a paste using an organic solvent orbinder. Exemplary negative CTE inorganic fillers include cordieriteparticles (e.g. Mg₂Al₃ [AlSi₅O₁₈]), barium silicates, β-eucryptite,zirconium vanadate (ZrV₂O₇), or zirconium tungstate, (ZrW₂O₈) and areadded to the glass frit, forming a paste, to lower the mismatch ofthermal expansion coefficients between substrates and the glass frit.The solvents are used to adjust the rheological viscosity of thecombined powders and organic binder paste and must be suitable forcontrolled dispensing purposes. To join two substrates, a glass fritlayer can be applied to sealing surfaces on one or both of thesubstrates by spin-coating or screen printing. The fit-coatedsubstrate(s) are initially subjected to an organic burn-out step atrelatively low temperature (e.g., 250° C. for 30 minutes) to remove theorganic vehicle. Two substrates to be joined are then assembled/matedalong respective sealing surfaces and the pair is placed in a waferbonder. A thermo-compressive cycle is executed under well-definedtemperature and pressure whereby the glass frit is melted to form acompact glass seal. Glass frit materials, with the exception of certainlead-containing compositions, typically have a glass transitiontemperature greater than 450° C. and thus require processing at elevatedtemperatures to form the barrier layer. Such a high-temperature sealingprocess can be detrimental to temperature-sensitive workpieces. Further,the negative CTE inorganic fillers, which are used in order to lower thethermal expansion coefficient mismatch between typical substrates andthe glass frit, will be incorporated into the bonding joint and resultin a frit-based barrier layer that is substantially opaque. Based on theforegoing, it would be desirable to form glass-to-glass, glass-to-metal,glass-to-ceramic, and other seals at low temperatures that aretransparent and hermetic.

While conventional laser welding of glass substrates can employultra-high laser power devices, this operation at near laser ablationoften times damages the glass substrates and achieves a poor qualityhermetic seal. Again, such conventional methods increase the opacity ofthe resulting device and also provide a low quality seal.

SUMMARY

Embodiments of the present disclosure are generally directed to hermeticbarrier layers, and more particularly to methods and compositions usedto seal solid structures using absorbing thin films. Embodiments of thepresent disclosure provide a laser welding or sealing process of a glasssheet with other material sheets using a thin film with absorptiveproperties during sealing process as an interfacial initiator. Exemplarylaser-welding conditions according to embodiments can be suitable forwelding over interfacial conductive films with negligible reduction inthe conductivity. Such embodiments may thus be employed to form hermeticpackages of active devices such as OLEDs or other devices and enablewidespread, large-volume fabrication of suitable glass or semiconductorpackages. It should be noted that the terms sealing, joining, bonding,and welding can be and are used interchangeably in the instantdisclosure. Such use should not limit the scope of the claims appendedherewith. It should also be noted that the terms glass and inorganic asthey relate to the modification of the noun film can be usedinterchangeably in this instant disclosure, and such use should notlimit the scope of the claims appended herewith.

Embodiments of the present disclosure provide a laser sealing process,e.g., laser welding, diffusing welding, etc., that can provide anabsorptive film at the interface between two glasses. The absorption insteady state may be greater than or as high as about 70% or may be lessthan or as low as about 10%. The latter relies upon color centerformation within the glass substrates due to extrinsic color centers,e.g., impurities or dopants, or intrinsic color centers inherent to theglass, at an incident laser wavelength, combined with exemplary laserabsorbing films. Some non-limiting examples of films include SnO₂, ZnO,TiO₂, ITO, UV absorbing glass films with Tg<600° C., and low meltingglass (LMG), or low liquidus temperature (LLT) films (for materialswithout a glass transition temperature) which can be employed at theinterface of the glass substrates. LLT materials may include, but arenot limited to, ceramic, glass-ceramic, and glass materials to name afew. LLT glass, for example, can include tin-fluorophosphate glass,tungsten-doped tin fluorophosphate glass, chalcogenide glass, telluriteglass, borate glass and phosphate glass. In another non-limitingembodiment, the sealing material can be a Sn²⁺ containing inorganicoxide material such as, for example, SnO, SnO+P₂O₅ and SnO+BPO₄.Additional non-limiting examples may include near infrared (NIR)absorbing glass films with absorption peaks at wavelength >800 nm. Weldsusing these materials can provide visible transmission with sufficientUV or NIR absorption to initiate steady state gentle diffusion welding.These materials can also provide transparent laser welds havinglocalized sealing temperatures suitable for diffusion welding. Suchdiffusion welding results in low power and temperature laser welding ofthe respective glass substrates and can produce superior transparentwelds with efficient and fast welding speeds. Exemplary laser weldingprocesses according to embodiments of the present disclosure can alsorely upon photo-induced absorption properties of glass beyond colorcenter formation to include temperature induced absorption.

The phenomenon of welding transparent glass sheets together with a laserusing an interfacial thin film of low melting inorganic (LMG) materialor ultraviolet absorbing (UVA) or infrared absorbing (IRA) material toinitiate sealing is described herein. In exemplary embodiments, threecriteria are described for realizing strong bond formation: (1)exemplary LMG or UVA or IRA films can absorb at an incident wavelengthoutside of window of transparency (from about 420 nm to about 750 nm)sufficient to propagate sufficient heat into the glass substrate, andthe glass substrate can thus exhibit (2) temperature-induced-absorptionand (3) transient color-center formation at the incident wavelength.Measurements suggest that a thermo-compressive diffusion weldingmechanism is formed, qualitatively resulting in a very strong bondformation. The unfolding of temperature events related to the weldingprocess and clear prevalence of color center formation processes inlaser welding are also described herein. CTE-mismatch irrelevancebetween the LMG or UVA material and Eagle XG® materials and post-weldstrength enhancement after thermal cycling to 600° C. are alsodiscussed. Embodiments are also discussed regarding the welding of glasssheets together that have different thicknesses by using thermallyconductive plates. Embodiments described herein can thus provide anability to form hermetic packages, with both passive and active devices,that can include laser sealing attributes associated with using LMG orUVA interfacial materials. Exemplary attributes include, but are notlimited to, transparent, strong, thin, high transmission in the visiblespectrum, “green” composition, CTE-mismatch irrelevance between LMG orUVA films and glass substrates, and low melting temperatures.

Additional embodiments of the present disclosure provide a laser sealingprocess having a low temperature bond formation and “direct glasssealing” where the transparent glass can be sealed to absorbing glass atthe incident wavelength resulting in an opaque seal at visiblewavelengths 400-700 nm. With exemplary embodiments, both glasses aretransparent or almost transparent at incident laser wavelengths, and inthe visible wavelength range. The resulting seal is also transparent inthe visible wavelength range making it attractive for lightingapplications as no light is absorbed at the seal location, and thus, noheat build-up is associated with the seal. In addition, since the filmcan be applied over the entire cover glass, there is no need toprecision dispense sealing frit paste for the sealing operation therebyproviding device manufacturers large degrees of freedom for changingtheir sealing pattern without need for special patterning and processingof the sealing area. In other embodiments, sealing can also be performedon certain spots of the glass area to form non-hermetic bonding formechanical stability. Furthermore, such sealing can be performed oncurved conformal surfaces.

Embodiments of the present disclosure provide low melting temperaturematerials which may be used to laser-weld glass sheet together thatinvolve welding any glass without regard to the differing CTEs of theglass. Additional embodiments can provide symmetric welding (i.e.,thick-to-thick) of glass substrates, e.g., Eagle-to-Eagle,Lotus-to-Lotus, etc. Some embodiments can provide asymmetric welding(i.e., thin-to-thick) of glass substrates, e.g., Willow-to-Eagle XG®,Eagle-to-Lotus (i.e., thin-to-thin), Eagle-to-Fused Silica,Willow-to-Willow, fused silica-fused silica, etc. using thermallyconductive plates. Further embodiments can provide disparate substratewelding (glass to ceramic, glass to metal, etc.) and can providetransparent and/or translucent weld lines. Some embodiments can providewelding for thin, impermeable, “green”, materials and can provide strongwelds between two substrates or materials having large differences inCTEs.

Embodiments also provide materials used to laser weld glass packagestogether thereby enabling long lived hermetic operation of passive andactive devices sensitive to degradation by attack of oxygen andmoisture. Exemplary LMG or other thin absorbing film seals can bethermally activated after assembly of the bonding surfaces using laserabsorption and can enjoy higher manufacturing efficiency since the rateof sealing each working device is determined by thermal activation andbond formation rather than the rate one encapsulates a device by inlinethin film deposition in a vacuum or inert gas assembly line. ExemplaryLMG, LLT and other thin absorbing films in UV or NIR-IR seals can alsoenable large sheet multiple device sealing with subsequent scoring ordicing into individual devices (singulation), and due to high mechanicalintegrity, the yield from singulation can be high.

In some embodiments, a method of bonding a workpiece comprises formingan inorganic film over a surface of a first substrate, arranging aworkpiece to be protected between the first substrate and a secondsubstrate wherein the film is in contact with the second substrate, andbonding the workpiece between the first and second substrates by locallyheating the film with laser radiation having a predetermined wavelength.The inorganic film, the first substrate, or the second substrate can betransmissive at approximately 420 nm to approximately 750 nm.

In other embodiments, a bonded device is provided comprising aninorganic film formed over a surface of a first substrate, and a deviceprotected between the first substrate and a second substrate wherein theinorganic film is in contact with the second substrate. In such anembodiment, the device includes a bond formed between the first andsecond substrates as a function of the composition of impurities in thefirst or second substrates and as a function of the composition of theinorganic film though a local heating of the inorganic film with laserradiation having a predetermined wavelength. Further, the inorganicfilm, the first substrate, or the second substrate can be transmissiveat approximately 420 nm to approximately 750 nm.

In further embodiments, a method of protecting a device is providedcomprising forming an inorganic film layer over a first portion surfaceof a first substrate, arranging a device to be protected between thefirst substrate and a second substrate wherein the sealing layer is incontact with the second substrate, and locally heating the inorganicfilm layer and the first and second substrates with laser radiation tomelt the sealing layer and the substrates to form a seal between thesubstrates. The first substrate can be comprised of glass orglass-ceramics, and the second substrate can be comprised of glass,metal, glass-ceramics or ceramic.

Additional features and advantages of the claimed subject matter will beset forth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the claimed subject matter as described herein,including the detailed description which follows, the claims, as well asthe appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the presentdisclosure, and are intended to provide an overview or framework forunderstanding the nature and character of the claimed subject matter.The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated into andconstitute a part of this specification. The drawings illustrate variousembodiments and together with the description serve to explain theprinciples and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

These figures are provided for the purposes of illustration, it beingunderstood that the embodiments disclosed and discussed herein are notlimited to the arrangements and instrumentalities shown.

FIG. 1 is a diagram of an exemplary procedure for laser weldingaccording to an embodiment of the present disclosure.

FIG. 2 is a schematic diagram illustrating the formation of ahermetically-sealed device via laser-sealing according to oneembodiment.

FIG. 3 is a diagram of another embodiment of the present subject matter.

FIG. 4 is an illustration of an experimental arrangement used toestimate physical extent of a laser welding bonding zone.

FIG. 5 is a microscopic image of fractured samples.

FIG. 6 is an illustration of a modeling scheme according to someembodiments of the present disclosure.

FIG. 7 is another modeling scheme according to embodiments of thepresent disclosure.

FIG. 8 is a diagram of an experimental arrangement for a 355 nm lasertransmission (% T) through Eagle 0.7 mm glass substrate for % T versustime measurements.

FIG. 9 is a plot according to an embodiment of the present disclosure.

FIG. 10 is a series of plots analyzing diffusion into an Eagle XG® glasssubstrate from an LMG film layer at the glass interface.

FIG. 11 is a schematic illustration of the performance of laser weldingbetween different thickness glass sheets.

FIG. 12 is an illustration of an experiment assessing the extent oflaser welding over ITO leads.

FIG. 13 provides photographs of laser seal lines formed over an ITOpatterned film.

FIG. 14 is a series of photographs of additional laser seal lines formedover a patterned film.

FIG. 15 is a simplified diagram of another method according to someembodiments.

FIG. 16 is a two-layer laser heating surface absorption model for someembodiments.

FIG. 17 is a series of temperature variation plots for some embodiments.

FIG. 18 is a series of plots of average energy deposited within asweeping laser's dwell time for some embodiments.

FIG. 19 is a plot of Eagle XG® and Lotus XT® glass transmission at 355nm during heating with an IR radiation source.

FIG. 20 is a plot of glass transmission at 355 nm during heating forsome embodiments.

FIG. 21 is a plot of the effect on film and substrate transmissionduring and after UV radiation for some embodiments.

FIG. 22 is a plot of absorption versus wavelength for some embodiments.

FIG. 23 is a photograph of a laser seal or bond line for an exemplarylow melting glass film on Eagle XG® glass.

FIG. 24 is a photograph of crossing laser seal lines for an exemplarylow melting glass film on Eagle XG® glass.

FIG. 25 is a schematic illustration of the range of interface contactgeometries observed while laser welding for some embodiments.

FIG. 26 is a schematic illustration of the evolution of relative contactarea, A_(c)/A₀, during laser welding of the interfacial gap region underconstant applied pressure P_(ext).

FIG. 27 illustrates a profilometer trace over a laser sweep region of anembodiment using typical laser welding conditions.

FIG. 28 is a series of plots providing a comparison of welding rateestimates for some embodiments.

FIG. 29 is a schematic illustration of polarimetry measurements andimages of some embodiments.

FIG. 30 is a plot providing stress location from an exemplary weld line.

FIG. 31 is a series of photographs of laser welded soda lime glassaccording to some embodiments.

FIG. 32 is a schematic illustration of some embodiments.

FIGS. 33 and 34 are photographs of weld lines in some embodiments.

While this description can include specifics, these should not beconstrued as limitations on the scope, but rather as descriptions offeatures that can be specific to particular embodiments.

DETAILED DESCRIPTION

Various embodiments for luminescent coatings and devices are describedwith reference to the figures, where like elements have been given likenumerical designations to facilitate an understanding.

It also is understood that, unless otherwise specified, terms such as“top,” “bottom,” “outward,” “inward,” and the like are words ofconvenience and are not to be construed as limiting terms. In addition,whenever a group is described as comprising at least one of a group ofelements and combinations thereof, the group can comprise, consistessentially of, or consist of any number of those elements recited,either individually or in combination with each other.

Similarly, whenever a group is described as consisting of at least oneof a group of elements or combinations thereof, the group can consist ofany number of those elements recited, either individually or incombination with each other. Unless otherwise specified, a range ofvalues, when recited, includes both the upper and lower limits of therange. As used herein, the indefinite articles “a,” and “an,” and thecorresponding definite article “the” mean “at least one” or “one ormore,” unless otherwise specified

Those skilled in the art will recognize that many changes can be made tothe embodiments described while still obtaining the beneficial resultsof the invention. It also will be apparent that some of the desiredbenefits of the present disclosure can be obtained by selecting some ofthe described features without using other features. Accordingly, thoseof ordinary skill in the art will recognize that many modifications andadaptations are possible and can even be desirable in certaincircumstances and are part of the invention. Thus, the followingdescription is provided as illustrative of the principles of the presentdisclosure and not in limitation thereof.

Those skilled in the art will appreciate that many modifications to theexemplary embodiments described herein are possible without departingfrom the spirit and scope of the invention. Thus, the description is notintended and should not be construed to be limited to the examples givenbut should be granted the full breadth of protection afforded by theappended claims and equivalents thereto. In addition, it is possible touse some of the features of the present disclosure without thecorresponding use of other features. Accordingly, the foregoingdescription of exemplary or illustrative embodiments is provided for thepurpose of illustrating the principles of the present disclosure and notin limitation thereof and can include modification thereto andpermutations thereof.

FIG. 1 is a diagram of an exemplary procedure for laser weldingaccording to some embodiments of the present disclosure. With referenceto FIG. 1, a procedure is provided for laser welding of two Eagle XG®(EXG) glass sheets or substrates together using a suitable UV laser.While two EXG glass sheets are illustrated and described, the claimsappended herewith should not be so limited as any type and compositionof glass substrates can laser welded using embodiments of the presentdisclosure. That is, methods as described herein are applicable to sodalime glasses, strengthened and unstrengthened glasses, aluminosilicateglasses, etc. With continued reference to FIG. 1, a sequence ofexemplary steps in laser-welding two glass substrates together isprovided whereby one substrate can be coated with a low melting glass(LMG) or ultraviolet absorbing (UVA) film material or NIR absorbing(IRA) film material. In steps A to B, a top glass substrate can bepressed onto another substrate coated with an exemplary UVA, IRA or LMGfilm. It should be noted that many experiments and examples describedherein may refer to a particular type of inorganic film (e.g., LMG, UVA,etc.). This, however, should not limit the scope of the claims appendedherewith as many types of inorganic films are suitable for the weldingprocesses described. In step C, a laser can be directed at an interfaceof the two glass sheets with suitably chosen parameters to initiate awelding process as illustrated in step D. The weld dimension was foundto be slightly less than the dimensions of the incident beam(approximately 500 μm).

FIG. 2 is a schematic diagram illustrating the formation of ahermetically-sealed device via laser-sealing according to oneembodiment. With reference to FIG. 2, in an initial step, a patternedglass layer 380 comprising a low melting temperature (e.g., low T_(g))glass can be formed along a sealing surface of a first planar glasssubstrate 302. The glass layer 380 can be deposited via physical vapordeposition, for example, by sputtering from a sputtering target 180. Inone embodiment, the glass layer can be formed along a peripheral sealingsurface adapted to engage with a sealing surface of a second glass orother material substrate 304. In the illustrated embodiment, the firstand second substrates, when brought into a mating configuration,cooperate with the glass layer to define an interior volume 342 thatcontains a workpiece 330 to be protected. In the illustrated example,which shows an exploded image of the assembly, the second substratecomprises a recessed portion within which a workpiece 330 is situated.

A focused laser beam 501 from a laser 500 can be used to locally meltthe low melting temperature glass and adjacent glass substrate materialto form a sealed interface. In one approach, the laser can be focusedthrough the first substrate 302 and then translated (scanned) across thesealing surface to locally heat the glass sealing material. To affectlocal melting of the glass layer, the glass layer can preferably beabsorbing at the laser processing wavelength. The glass substrates canbe initially transparent (e.g., at least 50%, 70%, 80% or 90%transparent) at the laser processing wavelength.

In an alternate embodiment, in lieu of forming a patterned glass layer,a blanket layer of sealing (low melting temperature) glass can be formedover substantially all of a surface of a first substrate. An assembledstructure comprising the first substrate/sealing glass layer/secondsubstrate can be assembled as above, and a laser can be used tolocally-define the sealing interface between the two substrates.

The laser 500 can have any suitable output to affect sealing. Anexemplary laser can be a UV laser such as, but not limited to, a 355 nmlaser, which lies in the range of transparency for common displayglasses. A suitable laser power can range from about 1 W to about 10 W.The width of the sealed region, which can be proportional to the laserspot size, can be about 0.06 to 2 mm, e.g., 0.06, 0.1, 0.2, 0.5, 1, 1.5or 2 mm. A translation rate of the laser (i.e., sealing rate) can rangefrom about 1 mm/sec to 400 mm/sec or even to 1 m/sec or greater, such as1, 2, 5, 10, 20, 50, 100, 200, or 400 mm/sec, 600 mm/sec, 800 mm/sec, 1m/sec. The laser spot size (diameter) can be about 0.02 to 2 mm.

Suitable glass substrates exhibit significant induced absorption duringsealing. In some embodiments, the first substrate 302 can be atransparent glass plate like those manufactured and marketed by CorningIncorporated under the brand names of Eagle 2000® or other glass.Alternatively, the first substrate 302 can be any transparent glassplate such as those manufactured and marketed by Asahi Glass Co. (e.g.,AN100 glass), Nippon Electric Glass Co., (e.g., OA-10 glass or OA-21glass), or Corning Precision Materials. The second substrate 304 can bethe same glass material as the first glass substrate, or secondsubstrate 304 can be a non-transparent substrate such as, but notlimited to, a ceramic substrate or a metal substrate. Exemplary glasssubstrates can have a coefficient of thermal expansion of less thanabout 150×10⁻⁷/° C., e.g., less than 50×10⁻⁷, 20×10⁻⁷ or 10×10⁻⁷/° C. Ofcourse, in other embodiments the first substrate 302 can be a ceramic,ITO, metal or other material substrate, patterned or continuous.

FIG. 3 is a diagram of another embodiment of the present subject matter.With reference to FIG. 3, the upper left diagram illustrates someexemplary parameters that can be employed to laser weld two Eagle XG®(EXG) glass substrates. The transmission, % T, can be monitored overtime and is illustrated in the lower left graph for three differentlaser powers. The onset of melting of the LMG, IRA or UVA film can bereadily observed in the lower laser power curves (rightmost curves) as a“knee” like inflection followed by rapid absorption and heating of theglass substrate, due to high local glass temperatures exceeding EagleXG®'s strain point. The inflection can be removed at higher laser powers(leftmost curve) and can induce a seamless transition from LMG, IRA orUVA absorption to glass fusion. Exemplary laser welding can includesweeping this zone along the interfacial boundaries to be bonded. Threecriteria are described in the list shown in the lower right corner andin greater detail below, e.g., low melting film absorbs/melts at anincident wavelength, color center formation in the glass, and/ortemperature induced absorption in the glass in some embodiments. Theabsorption of the film may be sufficient alone without effect of colorcenter formation or even temperature absorption effect. It should benoted that the order of events identified in FIG. 3 should not limit thescope of the claims appended herewith or be indicative of relativeimportance to the other listed events.

In some embodiments, the initiating event can be the UV laser absorptionby the low melting glass (e.g., LMG or UVA) film. This can be based uponthe larger absorbance of the thin film compared to Eagle XG® at 355 nmand the melting curves depicted in FIG. 3. Considering the experimentalarrangement illustrated in the top left portion of FIG. 3, the laser wasa Spectra Physics HIPPO 355 nm, generating 8-10 ns pulses at 30 kHz, upto 6.5 Watts of average power. The laser beam was focused to a 500micron diameter beam waist, and the transmitted beam was monitored andsampled, yielding plots of the transmission percentage (% T) with timefor different laser powers (5.0 W, 5.5 W, 6.0 W). These plots are shownin the lower left part of FIG. 3. The onset of melting of the UVA, IRAor LMG film can be readily observed in FIG. 3 at lower laser power(bottom and middle curves) as the knee like inflection followed by rapidabsorption and heating of the glass substrate, due to high local glasstemperatures, which exceed Eagle XG®'s strain point. The glass partsbeing welded may not be melted but are rather only softened so theybecome pliant when held in intimate contact with a modest applied force.This behavior can be similar to solid state diffusion bonding,particularly in the ability to form strong bonds at between 50-80% ofthe substrate's melting temperature. An optical cross sectional image ofthe solid-state bond's birefringence illustrates a distinct interfaceline between the two parts being welded (see, e.g., FIG. 4).

Another embodiment includes welding with a 355-nm pulsed laser,producing a train of 1 ns pulses at 1 MHz, 2 MHz or 5 MHz repetitionrates. When focusing the beam on the inorganic film into a spot between0.02 mm and 0.15 mm diameter and welding with speeds ranging from 50mm/s to 400 mm/s, defect-free bonding lines of approximately 60 μm toapproximately 200 μm were produced. Required laser powers can range fromapproximately 1 W to approximately 10 W.

With reference to FIG. 4, an experimental arrangement is illustratedwhich was used to estimate physical extent of laser welding bondingzone. With continued reference to FIG. 4, two Eagle XG® slides werelaser welded as previously described, mounted in a glass sandwich andcut with a diamond saw. This is illustrated in the left panel of FIG. 4.The resulting cross section was mounted in a polarimeter to measure theoptical birefringence resulting from local stress regions. This is shownin the right panel of FIG. 4. The lighter regions in this right panelindicate more stress. As illustrated in the right panel of FIG. 4, abonded region appeared having a physical extent on the order 50 microns.Further, there does not appear to be any base or substrate glassmelting, however, the bond formed between the two glass substrates wasvery strong. For example, the image in the center of the birefringenceimage cross section depicts a solid-state bond region extending deep (50microns) into the Eagle XG® substrate which illustrates a high sealstrength. Laser welding would include sweeping this zone along theinterfacial boundaries to be bonded.

FIG. 5 is a microscopic image of fractured samples. With reference toFIG. 5, the illustrated three dimensional confocal microscopic images offractured samples illustrate that the seal strength of embodiments ofthe present disclosure can be sufficiently strong such that failureoccurs by ripping out the underlying substrate (e.g., Eagle XG®substrate) material as deep as 44 μm (i.e., a cohesive failure). Noannealing was performed on the samples. FIG. 5 further illustrates afractured sample of a non-annealed laser welded embodiment subjected toa razor blade crack opening technique. A series of three dimensionalconfocal measurements were made, and a representative example is shownon the right side of FIG. 5. One feature of these confocal images showsthat the interfacial seal strength can be sufficiently strong so thatfailure occurs within the bulk of the substrate material, e.g., as deepas 44 μm away from the interface in this instance and in otherexperiments as deep as approximately 200 μm. In additional experiments,polarimetry measurements showed a residual stress occurring in thenascent laser weld (the same condition studied in FIG. 5) that wasannealed at 600° C. for one hour, resulting in a tenacious bondexhibiting no measurable stress via polarimetry. Attempts at breakingsuch a bond resulted in breakage everywhere else except the seal line ofthe welded substrates.

As noted in FIG. 3, strong, hermetic, transparent bonds can be achievedusing embodiments of the present disclosure by an exemplary low meltingfilm or another film that absorbs/melts at an incident wavelength, colorcenter formation in the film and glass, and temperature inducedabsorption in the film and glass. With regard to the first criterion,e.g., the low melting glass absorption event, laser illumination of theglass-LMG/UVA-glass structure with sufficiently high power per unit areacan initiate absorption in the sputtered thin film LMG/UVA interface,inducing melting. This can be readily observed in the bottom curve ofFIG. 3 in the lower left corner. The first downward slope of the bottomcurve tracks the LMG/UVA melting process out to about 15 seconds, atwhich point another process occurs, this one being a glass-laserinteraction (i.e., color center formation) in the respective substrate.The large curvature of this middle downward curve, after about 17seconds would indicate a large absorption resulting from color centersforming in the glass. These color centers can generally be a function ofthe elemental impurity content in the substrate, e.g., As, Fe, Ga, K,Mn, Na, P, Sb, Ti, Zn, Sn to name a few. The more curvature in thetransmission curve, the more color centers form. This is the secondcriterion noted in FIG. 3. The melting point of the LMG/UVA film can be,but is not limited to, about 450° C., but the interfacial temperaturecan likely be above 660° C. based upon observations of a laserillumination experiment with a surrogate aluminum-coated EXG glasssubstrate under similar laser welding conditions. In this experiment,the aluminum melted (melting temperature: 660° C.), and the surfacetemperature was measured with a calibrated thermal imaging camera (FLIRcamera) to be about 250° C. using laser welding conditions.

FIG. 6 is an illustration of a modeling scheme according to someembodiments of the present disclosure. With reference to FIG. 6, LMG/UVAand EXG material thermal transport properties were used to model a 355nm laser hitting a two-layer stack comprising 1 μm thin inorganicfilm+700 μm EXG, at 0.8-3 kW/cm². No phase change in the thin inorganicfilm (e.g., LMG, IRA, UVA film, etc.) was accounted for in the model.With continued reference to FIG. 6, estimates of the instantaneousthermal distribution were made suggesting interfacial temperaturesgreater than 660° C. can be achieved. Regardless of the exactinterfacial temperatures above 660° C. that are achieved, the presenceof the hot melted LMG/UVA interfacial film increases absorption in theglass substrate by shifting energy band gap to a lower energy. Theseband gap shifts are generally understood to arise from the thermalexpansion of the substrate lattice, related to the change of theelectron energies, and the direct renormalization of band energies dueto electron-photon interactions. A plot of this behavior in fused silicais shown in the lower right corner of FIG. 3. The net effect is that thehot LMG/UVA film drives more absorption in the EXG substrate near theinterface by lowering the band gap which in turn generates more heatfrom an internal conversion processes, lowering the band gap evenfurther. This process can be collectively referred to as thermallyinduced absorption which represents the third criterion identified inFIG. 3. Of course, other inorganic films can be used in such embodimentsand such examples should not limit the scope of the claims appendedherewith.

As noted above, color center formation plays a role in the formation oflaser welds according to embodiments of the present disclosure. Modelingthe basic color center formation processes under non-multiphotonconditions to derive a fitting function based on a three level diagramis illustrated in FIG. 7 using an experimental arrangement depicted inFIG. 8. FIG. 7 is another modeling scheme according to embodiments ofthe present disclosure. In the left panel of FIG. 7, three electronicglass band states absorb 355 nm photons, building up, or depletingpopulation in the ground state n_(g)[t], the conduction band n_(e)[t],and color centers n_(cc)[t]. It should be noted that single-headedarrows represent laser absorption, and double-headed arrows representboth stimulated absorption and emission. In the right panel of FIG. 7,rate equations are provided which predict the smooth monotonic build upand depletion of electronic level populations while the coherentlydriven parts of the system exhibit rapid oscillations of the samepopulations (n_(g) ↔n_(e)). The initial conditions of the three levelsare provided in the bottom row of the right panel of FIG. 7. FIG. 8 is adiagram of an experimental arrangement for a 355 nm laser transmission(% T) through an Eagle 0.7 mm glass substrate for % T versus timemeasurements. With reference to FIG. 8, diagnostic packaging can measureintegrated energy and temporal waveform of UV pulses after passingthrough a fused silica window and Eagle XG® glass sheet withapproximately 5 to 6 W being the average power.

Equation (1) below describes an experimental observable absorbance (Abs)versus time, e.g., related to transmission (trans) versus time data:(1≈Abs+Trans). The solution can be a sum of rising and decayingexponents, but can be simplified to following expression:

$\begin{matrix}{{{Ab}\;{s.}} \cong {{- \alpha} + {\alpha\;{{I\left( {\sigma_{g} - \sigma_{esa}} \right)} \cdot t}} + {\frac{\alpha\; I\;\sigma_{g}}{2}{\quad{\left\lbrack {{k_{ec}\left( {\sigma_{eas} - \sigma_{cc}} \right)} - {k_{f}\left( {\sigma_{esa} - \sigma_{g}} \right)} + {I\left( {\sigma_{esa}^{2} + {2\sigma_{esa}\sigma_{g}} - {2\sigma_{g}^{2}}} \right)}} \right\rbrack \cdot t^{2}}}}}} & (1)\end{matrix}$where α represents the linear absorption coefficient (cm⁻¹), Irepresents the laser flux (photons/cm²·sec), σ_(g) represents the groundstate absorption cross section (cm²), σ_(esa), represents excited stateabsorption cross section (cm²), σ_(cc) represents the color-centerabsorption cross section (cm²), k_(ec) represents the transient colorcenter rate, and k_(f) represents the fluorescence decay rate. Withreference to Equation (1) and FIG. 8, the role color center formationhas in embodiments of the present disclosure can be observed. FIG. 9 isa plot according to an embodiment of the present disclosure. Withreference to FIG. 9, a plot of Equation (1) is provided in the presenceof color center formation (the illustrated arc), and in the absence ofcolor center formation (the illustrated line) for certain, non-limiting,laser-glass interaction parameters: α=0.01 cm⁻¹, I=4.6·10⁻²¹ photons/cm²sec, σ_(g)=1.20×10¹⁷ cm², σ_(esa,)=1.21 10⁻¹⁷ cm², σ_(cc)=2.20 10⁻¹³cm², k_(ec)≈1.0×10⁷ sec⁻¹. Setting σ_(cc)=0, a linear dependence couldbe made. % Transmission was then formed by the relation that %Transmission=100−% Absorbance. As FIG. 9 illustrates, it follows thatsimply zeroing the color center formation term (i.e., setting σ_(cc)=0)transformed the arc to a line using reasonably selected parametervalues. Experimentally laser-welded glass substrates generally exhibitedthis curvature, including without limitation, Eagle XG®, Lotus XT®,Willow, and combinations Willow-to-Willow, Willow-to-Lotus, andWillow-to-Eagle.

FIG. 10 provides plots analyzing diffusion into an Eagle XG® glasssubstrate from an exemplary LMG film layer at the glass interface. Withreference to FIG. 10, TOF-SIMS was applied to analyze possible diffusioninto an Eagle XG® glass substrate from an LMG film layer at the glassinterface having an exemplary non-limiting composition (38% SnO, 40%SnF₂, 20% P₂O₅, 2% Nb₂O₅) and with a thickness of about 0.8 μm undersuitable laser-welding conditions. F and Sn line scans over the originalinterface (a, b) and over the interface subjected to laser welding (c,d) indicate the extent of diffusion away from the interface is smallwhile fluorine migrated approximately half a micron away from theinterface and, on average, the tin did not significantly move. Thus,FIG. 10 provides evidence illustrating the lack of significantLMG-material diffusion into an exemplary substrate. Similar findings arealso observed with other exemplary inorganic thin films (UVA, IRA,etc.). While one might expect significantly more diffusion of mobileatomic species utilized in embodiments of the present disclosure on thebasis of the apparent large CTE mismatch between the interfacialmaterials, CTE_(870CHM)=18 ppm/° C. versus CTE_(EXG)=3.1 ppm/° C., nodelamination was observed. Rather, repeated cycling of temperatures ashigh as 600° C. appeared to remove any residual stress, resulting in astronger bond. The resulting inorganic thin film was sufficiently thinthat the delamination forces due to CTE mismatch in the respective glasssubstrates were much less than the bonding forces. This corresponds tothe knowledge that a laminate structure's composite stress from anadhered film's deposition-stress scales with the cube of the filmthickness.

FIG. 11 is a schematic illustration of the performance of laser weldingbetween different thickness glass sheets. With reference to FIG. 11, itwas discovered that welding ultra-thin Willow glass (0.1 mm) to EagleXG® glass (0.7 mm), i.e., an “asymmetric” case, a poor weld can result.In a “symmetric” Eagle-to-Eagle case (left side of FIG. 11), a thermallyhot zone was swept along the glass interface to perform a superior weld.A respective temperature distribution is illustrated below eachdepiction. When using dissimilarly thick glass sheets, an asymmetricthermal zone, however, occurs that can result in a poor weld in somecases, e.g., when welding Willow-to-Eagle (middle diagram of FIG. 11).Exemplary embodiments, however, can provide a solution to thisasymmetric welding problem which is illustrated on the right side ofFIG. 11 with use of a thermally conductive plate that can dissipate anyheat and cool the thin glass sheet to effectively restore the thermalhot zone resulting in the formation of a strong welded bond. Thus, someembodiments herein described can employ the use of thermally conductiveplates to laser weld glass sheets having different thicknesses.

While the description heretofore has described laser welding of glass toglass substrates (of similar or different dimensions, geometries, and/orthicknesses), this should not limit the scope of the claims appendedherewith as embodiments are equally applicable to substrates or sheetsof non-glass materials, such as, but not limited to ceramics,glass-ceramics, metals, and the like with, or without, an interfacialconductive film. For example, FIG. 12 is an illustration of anexperiment assessing the extent of laser welding over ITO leads. Withreference to FIG. 12, an LMG-coated Eagle XG® slide is illustrated laserwelded to an ITO-coated Eagle XG® slide in the left panel of the figure.In this experiment, a 100 nm ITO film was deposited onto Eagle XG®substrates by reactive sputtering through a mask. Conditions wereselected resulting in ITO films having a relatively high average sheetresistance of approximately 126Ω per square (Ω/sq), with astandard-deviation of 23 Ω/sq, reflecting that no thermal heating of thesubstrate was employed, before, during or after, the reactive sputteringdeposition. The ITO film appears in FIG. 12 as a distinct yellowish orshaded strip, diagonally distributed in the photograph. Multimetermeasurements of 350Ω were recorded over the distance indicated, prior tolaser welding. An LMG-coated Eagle XG® slide was then laser welded to anITO-coated Eagle XG® slide whereby it was discovered that the laser weldline was quite distinct, strong, transparent, and diagonally distributedbut inverted. In the right panel of FIG. 12, post laser-weld measurementof the resistance across the ITO leads over the same distance usedearlier was observed to increase the resistance from 350Ω to 1200Ω. Thedrop in conductivity was due to partial damage of the ITO film as theITO film absorbed 355 nm radiation. To avoid damage of ITO film due tooverheating, however, embodiments can change laser parameters sotemperature at the interface does not transition from bare glasssubstrate to ITO film substrate or otherwise (e.g., variable peak power,variable repetition rate, variable average power, variable translationspeed of the beam, electrode pattern, LMG film thickness, etc.).

FIG. 13 provides additional photographs of laser seal lines formed overan ITO patterned film. With reference to the left panel of FIG. 13,another electrode type was obtained from a different source, again madefrom ITO and having a thickness of approximately 250 nm. The ITO filmwas continuous, over which seals were formed using methods describedherein. The initial resistance, over an approximate 10 mm distance, wasmeasured at 220 Ohms. Laser sealing was performed at constant speed andpower when transitioning from the clear glass to the electrode area.After sealing was performed, a strong seal was observed over both clearglass and ITO regions, with the seal over ITO being slightly wider byapproximately 10-15%. Such an increase in seal width may suggest thatthere is more heat generated in this region than in the clear area.Additional heat generation can also be caused by absorption of theelectrode material by the laser radiation or by different thermaldiffusivity properties of the film, and in any case, resistance wasmeasured to increase approximately 10% to 240Ω which is insignificant.This can also indicate that when the temperature was raised relative tobare glass, the higher quality ITO and thicker film did not exhibitconductivity degradation. It should be noted that lowering the lasersealing power when it transitions from the clear glass to the electrodearea can reduce extra heat generation and therefore decrease resistivitydegradation in ITO. Experimental results also suggest that a singleelectrode split into an array of electrodes (having the same total widthas the original electrode) at the seal location(s) can be optimal whenusing an electrode width between ½-⅓ of the laser beam width, andspacing between ½-⅓ of the beam diameter. Later experiments conductedwith an increased sealing speed above 20 mm/s showed that resistancedegradation was less <1-2% after sealing with a starting resistance ofabout 200Ω.

FIG. 14 is a series of photographs of additional laser seal lines formedover a patterned film. With reference to FIG. 14, similar experimentswere performed with a non-transparent molybdenum metal electrode. FIG.14 provides a series of photographs of continuous and patternedmolybdenum interfacial film are shown over which laser seal lines wereformed. In the left panels, a photograph of a continuous molybdenum filmillustrates a more heterogeneous bond formation with cracked or brokenmolybdenum electrode portions. Even in this case, at constant lasersealing power, the uniform molybdenum electrode was not completelydamaged. However, due to laser radiation absorption or reflection by theuniform electrode, the heating was substantially higher at the electrodearea than in the clear glass region. This can be observed by theincreased width area of the seal over the molybdenum region. It shouldbe noted that one area that was undamaged was at the transition zonebetween the clear and uniform molybdenum areas thereby suggesting thatpower adjustment, laser power density, laser spot speed, or combinationof all three factors during the sealing event can overcome anyoverheating effect for a uniform molybdenum electrode. In the rightpanel of FIG. 14, a photograph of a patterned or perforated molybdenumfilm illustrates a more homogeneous bond formation resulting in minimalperturbation to its conductivity, namely, 14Ω before welding to 16Ωafter welding. The sealing over this perforated region exhibited muchless heating and therefore presents an alternative to the powermodulation method. It should also be noted that electrode metals shouldbe carefully selected as it was discovered that sealing with metalshaving a low melting temperature (Al) are unlikely to survive thesealing conditions, in comparison to molybdenum (650° C. vs. 1200° C.)or other metals having a high melting temperature. Thus, the resultssuggest that a single electrode split into an array of electrodes(having the same total width as the original electrode) at the seallocation can be optimal when using an electrode width between ½-⅓ of thelaser beam width and spacing between ½-⅓ of the beam diameter. Thus,embodiments of the present disclosure are applicable to laser sealing ofglass to glass, metal, glass-ceramic, ceramic and other substrates ofequal or different dimensions, geometries and thicknesses.

Applications that may utilize embodiments described herein havingefficient formation of high bond-strength, transparent, glass-to-glasswelds are numerous and include, but are not limited to, solid statelighting, display, and transparent vacuum insulated technologies. Laserwelding of glass, in particular, can provide efficiencies and featuressuch as a small heat affected zone (HAZ) that many traditional weldingmethods, such as e-beam, arc, plasma, or torch simply cannot provide. Insome embodiments, laser glass welding can generally proceed without pre-or post-heating using infrared (IR) lasers for which many glasses areopaque or ultra-short pulse lasers (USPL) for which many glasses aretransparent. In some embodiments, a judicious choice of glass substratecompositions and interfacially distributed IR absorbing frit can makehermetic glass “sandwich-type” laser sealed packages possible. In someembodiments, ultra-short pulsed lasers can be focused at either surfaceor interior points in an exemplary glass substrate and can induceabsorption by non-linear processes such as multi-photon or avalancheionization.

Heretofore, a low-power laser-welding process has been described thatrelies on an absorbing low melting glass interfacial film and can beattributed to diffusion welding, owing to its low temperature bondformation (as low as half the melting temperature), and requirement forcontact and pressure conditions. As discussed above, several effectswere notable to laser welding glass sheets together with strong bondformation, e.g., an absorbing low melting glass film at the incidentlaser wavelength, laser induced color centers formed in the glasssubstrates, and thermal induced absorption in the substrate toeffectively accelerating the temperature increase.

In some embodiments, however, many films highly absorbing at an incidentwavelength (e.g., 355 nm) can be sufficient to induce high bond strengthlaser welds. Other films, for example, ZnO or SnO₂, are chemicallydifferent than some exemplary low melting glass compositions describedherein but share the same laser welding capability at a relatively lowlight flux. Thus, it was discovered that the low melting character maynot be necessary in some embodiments, in light of the meltingtemperature of ZnO (1975° C.) as compared with some low melting glasscompositions (˜450° C.). It was discovered, however, that a unifyingcharacteristic of these films was that they absorb radiationsubstantially at 355 nm: ZnO absorbance ˜45% (200 nm thick film), andlow melting glass ˜15% (200 nm thick film). It was also determined thatexemplary methods described herein could laser weld quartz, or purefused silica substrates—i.e., substrates without color centers. Thus, ithas been determined that color centers are not necessarily essential butmay be needed in some embodiments when absorption of an exemplary filmis low (e.g., ˜Abs<20%).

FIG. 15 is a simplified diagram of another method according to someembodiments. With reference to FIG. 15, a defocused laser 15 with adefined beam width w is incident on a sandwich-type structure 16 formedfrom contacting two sheets of glass 17, 18, with one sheet's interiorinterface coated with a thin absorbing film 19. While the beam isillustrated as cylindrical, such a depiction should not limit the scopeof the claims appended herewith as the beam can be conical or anothersuitable geometry. The film material can be selected for its absorbanceat the incident laser wavelength. The laser 15 can be translated at apredetermined speed, v_(s), and the time the translating laser beam caneffectively illuminate a given spot and can be characterized by thedwell time, w/v_(s). In some embodiments, modest pressure can be appliedduring the welding or bonding event, ensuring a sustained contactbetween the clean surfaces, while any one or several parameters areadjusted to optimize the weld. Exemplary, non-limiting parametersinclude laser power, speed v_(s), repetition rate, and/or spot size w.

As noted above with reference to FIG. 3, it was discovered that optimumwelding can be a function of three mechanisms, namely, absorption by anexemplary film and/or substrate of laser radiation and the heatingeffect based of this absorption process, increase of the film andsubstrate absorption due to the heating effects (band gap shift to thelonger wavelength) which can be transient and depends upon theprocessing conditions, and defect or impurity absorption or color centerabsorption generated by UV radiation. Thermal distribution can be animportant aspect of this process, and the discussion below can be usedto assist in the understanding of temperature distribution at theinterface between two substrates, assuming static absorption at theinterface.

El-Adawi developed an analytical model of laser-heating a two-layerstack consisting of an absorbing film of thickness Z, on a largesemi-infinite slab substrate. The heat diffusion equation in eachmaterial was solved with matched boundary conditions yieldingexpressions of temperature as a function of time and position with thefilm and substrate: T_(f)(t, z), T_(s)(t, z). El-Adawi's model assumedthermal properties (diffusivity, D, conductivity, k, heat capacity,C_(p)) of the film and substrate were fixed, such that absorptionoccurred only in the surface and no phase changes occurred. Laplacetransforms were used yielding summations with exponential and error(complementary) function terms:

$\begin{matrix}{{{T_{f}\left( {z_{f},t} \right)} = {{\sum\limits_{n = 0}^{\infty}{\frac{I_{0}A_{f}}{k_{f}}{B^{n + 1}\left\lbrack {{\frac{L_{f}}{\sqrt{\pi}}e^{- \frac{a_{n}^{2}}{L_{f}^{2}}}} - {a_{n} \cdot {{erfc}\left( \frac{a_{n}}{L_{f}} \right)}}} \right\rbrack}}} + {\sum\limits_{n = 0}^{\infty}{\frac{I_{0}A_{f}}{k_{f}}{B^{n}\left\lbrack {{\frac{L_{f}}{\sqrt{\pi}}e^{- \frac{b_{n}^{2}}{L_{f}^{2}}}} - {b_{n} \cdot {{erfc}\left( \frac{b_{n}}{L_{f}} \right)}}} \right\rbrack}}}}}{{T_{s}\left( {z_{s},t} \right)} = {\sum\limits_{n = 0}^{\infty}{\frac{2I_{0}A_{f}}{k_{f}}{\frac{B^{n}}{\left( {1 + ɛ} \right)}\left\lbrack {{\frac{L_{f}}{\sqrt{\pi}}e^{- \frac{g_{n}^{2}}{L_{f}^{2}}}} - {g_{n} \cdot {{erfc}\left( \frac{g_{n}}{L_{f}} \right)}}} \right\rbrack}}}}} & (2)\end{matrix}$where A_(f) represents the surface absorbance of the thin film, I_(o)represents the laser flux (photons/cm²·sec), n represents an integer(0≤n≤∞), and all subscripts, f, refer to the film parameters whilesubscripts, s, refer to the substrate's parameters. B, and ε are relatedto material properties: B=1−ε/1+e<1, ε=(k_(s)/k_(f))√D_(f)/D_(s)), whileL_(f) also includes time t: L_(f) ²=4D_(f)t. The time and space rangefor the thin film layer can be provided as: 0<t, 0≤z_(f)≤Z,respectively, where Z represents the film thickness. The time and spacerange for the substrate layer are provided as: t_(s)<t, Z≤z_(s)≤∞,respectively, where t_(s) represents the time it takes the temperatureof the film's backside to begin deviation from room temperature afterinitial laser-film incidence (t_(s)=Z²/6D_(f)). Expansion coefficientsare related to independent variables and material properties through thefollowing expression:

$\begin{matrix}{{a_{n} = {{2{Z\left( {1 + n} \right)}} - z_{,}}},{b_{n} = {{2{nZ}} + z_{f}}},{g_{n} = {{\left( {1 + {2n}} \right)Z} + {z_{s}\sqrt{\frac{D_{f}}{D_{s}}}}}}} & (3)\end{matrix}$

FIG. 16 is a two-layer laser heating surface absorption model for someembodiments. With reference to FIG. 16, a pulsed UV (355 nm) laser 20 isillustrated striking a two-layer stack 22 having a 1 μm UVabsorbing-film 23 and a 700 μm Eagle-XG substrate 24. Spatialtemperature distribution away from the weld interface in the Eagle-XGstack 22 can be calculated from Equation (2) and plotted assuming apulsed (30 kHz, 10 ns pulse width, 500 μm wide laser beam-waistdiameter) 355 nm laser which delivers an average power of 6 Watts.Different laser sweep speeds (2 mm/s, 5 mm/s, 10 mm/2 and 20 mm/s) werethen used. A UV film absorbance of 15% was employed for the calculation,a value typical of tin-fluorophosphate LMG materials at 355 nm with athickness of about 200 nm. This temperature distribution in the EagleXG® substrate or stack 22 was plotted whereby temperature distributionvariations due to using different laser sweep speeds was observed as aslow moving laser beam dwells over a given laser weld site longer ascompared with faster moving beams. For example, the effective time a 500μm wide laser beam, moving at 2 mm/s dwelled over a given weld spot was0.25 seconds while the 20 mm/s sweeping laser beam dwelled only 0.025seconds.

Temperature variations due to using different laser powers, or filmswith differing absorbance were also explored as illustrated in FIG. 17.FIG. 17 is a series of temperature variation plots for some embodiments.With reference to FIG. 17, glass substrate temperature distributiondependence on laser power and film absorbance was plotted using thetwo-layer laser-heating model (Equation (2)). The same laser parametersused in FIG. 16 were used in FIG. 17. More specifically, a pulsed UVlaser with the following parameters was used: λ=355 nm, beam waist=500μm, repetition rate=30,000 Hz, and pulse width=10 ns. As can be observedin the left panel of FIG. 17, the influence of laser power on thesubstrate temperature distribution appears more linear as compared withthe higher order behavior of absorbance in the right panel of FIG. 17.This behavior is not obvious from Equation (2) where power, I_(o), andabsorbance, A_(f), appear coupled. Absorbance can indirectly impact theeffective film thickness, z_(f), for which the expansion coefficientsb_(n) and g_(n) are somewhat related. In contrast, I_(o) is independent,with no functional relationship associated with the expansioncoefficients b_(n), and g_(n).

FIG. 18 is a series of plots of average energy deposited within asweeping laser's dwell time for some embodiments. With reference to FIG.18, it can be observed that dwell time is dependent on both laser sweepspeed and laser pulse repetition rate, whose values and units areindicated in the independent variable x-y plane. These calculationsassume a film absorbance of 25%, 500 micron laser beam width, and 10 nslaser pulse width—that can result in successful laser glass welds insome embodiments. Threshold power (11 a for 6 W, 12 a for 20 W), thatpower above which successful laser welding occurs, is indicated in FIG.18 with the depicted plane, and empirically estimated from experiments.The top and bottom plots or panels vary in the amount of laser powerused: 6 Watts versus 20 Watts. Comparison of both plots in FIG. 18suggests that slight variation in laser speed and repetition rate at lowincident laser powers (e.g., 6 Watts) can incur substantially higherincident powers than is necessary to induce adequate laser welds. Evensmall excursions away from the initial laser-weld condition (30 kHz, 2mm/s laser sweep velocity) in the direction of higher repetition ratewould result in unnecessary incident power densities. Higher laser sweepspeeds rapidly provided inadequate amounts of energy required to laserweld the glass substrates which is a consequence of the inversedependence of laser dwell time on velocity versus the linear dependenceon laser repetition rate. At higher incident laser powers (e.g., 20Watts), a larger plateau region or process window 11 b, 12 b becomesavailable where small excursions in speed and repetition rate retainadequate laser welding conditions without excess energy being incurred.The process windows 11 b, 12 b for both plots can facilitate laserwelding or bonding optimization.

FIG. 19 is a plot of Eagle XG® and Lotus XT® glass transmission at 355nm during heating with an IR radiation source. With reference to FIG.19, effects of temperature change on the absorption properties of theglass interface was determined through experimentation when Eagle XG®and Lotus XT® substrates were irradiated with an infrared CO₂ laser at10.6 μm. It can be observed that the resulting transmission of thesesubstrates at 355 nm changed significantly depending upon temperaturegenerated by the CO₂ laser radiation. It follows that interface heatingin some embodiments can lead to a more effective absorption at theinterface in both the film as well as the glass substrate.

FIG. 20 is a plot of glass transmission at 355 nm during heating forsome embodiments. With reference to FIG. 20, it was discovered thatcolor center formation due to UV radiation can occur in both the filmand glass substrate which can lead to additional absorption in theradiated area. The effect of 355 nm transmission on Eagle XG® and LotusXT® glass substrates can be observed in FIG. 20 due to the resultanttemperature increase. The temperature increase can be attributed to acombination of the effect of heating shown in FIG. 19 and color centerformation.

FIG. 21 is a plot of the effect on film and substrate transmissionduring and after UV radiation for some embodiments. With reference toFIG. 21, the first curve 30 represents the transmission of an Eagle XG®0.6 mm substrate with a 200 nm ZnO film. A second curve 31 representstransient absorption due to 3 W/mm² radiation with a 355 nm lasersource, 30 kHz repetition rate (i.e., absorption on top of existingabsorption). This second curve 31 includes induced absorption due tocolor centers and temperature. A third curve 32 represents inducedabsorption after laser radiation is off, i.e., the temperature hasrecovered to ambient conditions, and color centers have partiallyvanished. It should be noted that there are some permanent absorptionchanges in these embodiments which have high transmissions at 420 nm andabove. This effect is due to the film presence and is significantlyamplified versus a bare substrate without film. Some changes in the filmand substrate can be permanent as observed in the third curve 32, butthis does not affect visible transmission. In addition to these UV-basedradiation effects, it can be observed that a desired temperature riseand fusion can occur based on absorption of the film alone, and thiseffect can also be realized with IR absorbing films as will be discussedbelow. Thus, as illustrated in FIG. 21, some exemplary films can exhibittemperature and color center formation as a function of temperature andpower density of UV radiation.

FIG. 22 is a plot of absorption versus wavelength for some embodiments.With reference to FIG. 22, an embodiment included a film made with anFeO based glass, which can be in two different oxidation states 2+ and3+ depending upon processing conditions. This exemplary, non-limitingsilica based glass film has greater than about 10-15 wt. % FeO with anequal proportion thereof being FeO and Fe₂O₃. As illustrated in FIG. 22,it was discovered that the Fe₂O₃ exhibited strong absorption at NIRwavelengths and could also be irradiated with a YAG laser at awavelength of 1064 nm. The visible transmission in this case is lessthan about 0.02 and does not compromise attenuation between about 420 nmto about 700 nm. Absorption at 1064 nm was found to be about 0.1 and theexemplary film could be heated with sufficient laser power above itsmelting point and laser welded. Of course, the claims appended herewithshould not be so limited as other examples of IR absorption films andother IR lasers are envisioned.

FIG. 23 is a photograph of a laser seal or bond line for an exemplarylow melting glass film on Eagle XG® glass. FIG. 24 is a photograph ofcrossing laser seal lines for an exemplary low melting glass film onEagle XG® glass. FIGS. 33 and 34 are photographs of weld lines in someembodiments. With reference to FIGS. 23, 24, 33 and 34 exemplary weldsmade with a UV laser at different conditions are illustrated. Morespecifically, FIG. 23 illustrates a 200 μm laser seal line using a 1 μmthick low melting glass film on Eagle XG® glass, and FIG. 24 illustratesthe crossing of two 400 μm lines using a 1 μm thick low melting glassfilm on Eagle XG® glass. The width of the weld, seal or bond lines canbe varied by modification of the spot size at the interface of therespective substrates. It was also noted during experimentation that nocracks in either the film or substrates were formed in either instance(single or crossing welds). With reference to FIG. 33, laser weld linescan be observed in a Lotus XT® glass stack having 1 μm low melting glassfilm intermediate the two substrates. Welding conditions included a 1MHz repetition rate, 10 W laser power, and 100 mm/s translation speedresulting in a 190 μm line width. With reference to FIG. 34, crossinglaser weld lines in an Eagle XG® glass stack having a 1 μm low meltingglass film can be observed. Welding conditions included a 1 MHzrepetition rate, 4 W laser power, and 200 mm/s translation speedresulting in an 80 μm line width.

FIG. 25 is a schematic illustration of the range of interface contactgeometries observed while laser welding for some embodiments. Withreference to FIG. 25, the left panel represents an interface conditionoccurring in an “Ra” range where thickness of the gap t_(gap) isdominated by the local surface roughness, statistically characterized bythe Ra number, with in-plane spatial distribution of asperitiescharacterized by a spatial correlation length. The right panel of FIG.25 represents an interface condition occurring in a “dirt” range wherethickness of the gap t_(gap) is dominated by the statistics ofprevailing dirt particle-size distribution, with in-plane spatialdistribution dominated by dirt density distribution. Thus, it can beobserved that gap thickness in the Ra range is dependent on the glasssubstrate surface statistics, ranging from ultra-smooth values as low asfractions of a nanometer (e.g., crystalline range), to tens ofnanometers at the upper range representing values typical ofcommercially available glass (e.g., soda lime, boro-silicates).

Exploring a potential mechanism underlying laser welding dynamics,diffusion-weld creep flow, it can be observed that relatively lowtemperature bond formation occurs as low as half the melting temperatureof the glass substrates, and that contact and pressure conditions may berequired in some embodiments. Mass transport of mostly substratematerial into the gap occurs in a manner consistent with hot swellingexpanding glass activated by temperatures above the substrate strainpoint. The movement of this material can be described by one of variousforms of creep flow typically found in diffusion welding models, namely,viscous, plastic, or diffusive transport processes. While these modelsare often used in the description of metal welding, they can be adaptedfor the present case, using the notion of relative contact area,A_(c)/A₀, and its kinetic development illustrated in FIG. 26. FIG. 26 isa schematic illustration of the evolution of relative contact area,A_(c)/A₀, during laser welding of the interfacial gap region underconstant applied pressure P_(ext). With reference to FIG. 26, in the toppanel, time=0 and the initial condition of the relative contact areaA_(c)/A₀=0. In the middle panel, time is greater than 0 illustrating anintermediate state of the interfacial gap region where A_(c)/A₀>0. Inthe bottom pane, time is at a predetermined point (t end) where the weldor bond is essentially complete and the gap is effectively non-existent,A_(c)/A₀,≈1. Formation of a diffusion-welded interface typified by FIG.26 assumes an evolution of relative contact area, A_(c)/A₀, thatconverges to distances at which chemical bonds form. An approximationcan be employed to describe these kinetics:

$\begin{matrix}{\frac{A_{c}}{A_{o}} = {{1 - {\exp^{- \frac{t}{t^{*}}}\mspace{14mu}{where}\mspace{14mu} t^{*}}} = {{k \cdot p^{n}}e^{\frac{Q}{R \cdot T}}}}} & (4)\end{matrix}$where k represents a constant, p represents pressure, n represents apressure exponent, and Q represents an activation energy of the specificrate-controlling creep-flow mechanism. The value of n can be correlatedwith the rate-controlling mechanism as follows: n=1, for viscous masstransport; n=2, for plastic flow; n=3, for evaporative/condensationtransport; and n>3, for diffusive transport.

Equation (4) can be employed as a guide in deducing some mechanisticforces at work since the expression assumes isothermal conditions. Tobegin this mechanistic exploration and because of its similarity toEagle XG® (softening point: 971° C.), parameters can be used from theliterature of a 3-point bend experimental study over the range from 800°C.-950° C., of the high temperature creep of low softening-pointboro-silicate glass (700° C.-750° C.) where it was found, for all stagesof creep, that deformation behavior exhibited linear viscoelasticitycontrolled by viscous flow for both fast and slow creep regimes. Usingfast creep regime data (n=1, Q=160 kJ/mol, and k=0.00048 Pa⁻¹s), withconditions similar to some laser welding experiments (950° C.), thetotal effective pressure of the weld area can be estimated, P_(total),at 950° C. as 600 MPa assuming Eagle XG®'s nominal modulus and CTEvalues of 73.6 GPa and 3.1 ppm/° C. apply, beyond that of the nominalapplied pressure of about 0.1 MPa. This upper bound estimation was basedon experimental data measured indicating substrate glass, and filmmaterial, swelling and expanding above the planar interface region asillustrated in FIG. 27. FIG. 27 illustrates a profilometer trace over alaser sweep region of an embodiment using typical laser weldingconditions. With reference to FIG. 27, the bottom schematic represents asingle low melting glass coated (1 μm thick film) Eagle XG® substratesubjected to two successive laser sweeps under the following conditions:355 nm, 30 kHz, 4 mm/sec translation rate. The top image of FIG. 27 is asingle-line profilometer trace over these two weld regions indicating araised morphology.

Even assuming temperature is fixed at 950° C., it may be noted whetherthe viscous flow mechanism under that condition is sufficient in formingand driving diffusion welds to completion (A_(c)/A₀≈1). FIG. 28 providessome insight to this case. FIG. 28 is a series of plots providing acomparison of welding rate estimates for some embodiments. Withreference to FIG. 28, a comparison of welding rate estimates can bebased upon Equation (4) using low strain and softening pointboro-silicate glass creep flow parameters and an effective weldingpressure of 600 MPa. The two plots differ only in assuming eitherviscous flow prevails (left plot) or plastic flow (right plot).Recalling that dwell times on the order of 0.25 seconds yield stronglaser welds under about 6 Watts and 30 kHz laser repetition rateconditions, the viscous flow interpretation may be questioned, and theleft plot in FIG. 28 suggests other mechanisms, e.g., plastic flow, thatmay also account for the strong weld formation.

FIG. 29 is a schematic illustration of polarimetry measurements andimages of some embodiments. With reference to FIG. 29, residual stressfields resulting from an exemplary laser welding process near theinterfacial weld bond can be examined. For example, the top panels ofFIG. 29 illustrate a polarimetry measurement of stress field in thevicinity of a laser weld between two 0.7 mm Eagle XG® glass substrates,with one interior surface coated with a 1 μm thick low melting glassfilm. The upper left panel provides a polarimetric image of residualstress field from a laser weld obtained from sweeping a 355 nm UV laserunder the following conditions: 20 mm/sec, 14 Watts, 200 μm beam width,and 150 kHz repetition rate, and the upper right panel provides a threedimensional rendering of this residual stress field. In the bottom panelof FIG. 29, an illustration is provided showing a propagating stressfield and the analytic dependence sought of its location from laser weldconditions. Influences on the location of the propagating stress fieldunder the prevailing laser weld conditions can then be estimated.Analytical models, however, tend to treat simple structures as asemi-infinite solid or slab. Equation (2) illustrates how complicatedsolutions can be for two-layer systems, which can rapidly becomeintractable with the introduction of a time dependent melt or stressfront. One model of melting considered a slab connected to a heat sinkwith the incident laser radiation entirely absorbed at the surface. Thismodel considered two time regimes: one regime where the melting time wasless than the transit time (e.g., the time it took for the back end ofthe slab to increase from room temperature), and the second regime formelting times greater than the transit time. This model also envisioneda heat balance equation applied to a propagating interface betweenliquid and solid:

$\begin{matrix}{{{I_{0} \cdot {A\left( {1 - R} \right)}} + {k\frac{dT}{dz}}} = {{\rho \cdot Q_{L}}\frac{dZ}{dt}}} & (5)\end{matrix}$where terms are identical with those used in Equation (2), except that Zrepresents the melt front location, Q_(L) represents the latent heat ofmelting, and that heat flow is one dimensional, optical radiation isabsorbed at the surface, and thermal material properties remaintemperature independent. Quadratic equations can then be derived in bothZ and dZ/dt having coefficients that are functions of thermo-physicaland laser parameters. To understand dependences of a propagating stressfield, the propagating laser melt front analytic model may be modifiedby substituting the latent heat of melting (fusion) of Eagle XG® withthe activation energy for creep flow from our previous Eagle XG®surrogate: the low strain point boro-silicate glass normalized with itseffective molecular weight (160 kJ/mol)/(0.266 kg/mol). Considering thecase where no heat is dissipated from the back of the slab substrateduring the weld, the resulting expression exhibits interestingdependencies on laser and material properties:

$\begin{matrix}{Z = {l - \frac{\sqrt{\begin{matrix}{C_{p}l^{2}I_{o}{{A\left( {1 - R} \right)} \cdot \rho^{3} \cdot}} \\\left\lbrack {{C_{p}l\;{\rho\left( {{{l \cdot I_{o}}{A\left( {1 - R} \right)}} + {6{\lambda \cdot \Delta}\; T_{m}}} \right)}} - {6{\lambda \cdot I_{o}}{{A\left( {1 - R} \right)} \cdot t}}} \right\rbrack\end{matrix}}}{{\sqrt{3} \cdot I_{o}}{{A\left( {1 - R} \right)} \cdot C_{p} \cdot l \cdot \rho^{2}}}}} & (6)\end{matrix}$where Z represents creep front location, l represents substratethickness, Cp represents substrate heat capacity, A represents substrateabsorbance, R represents substrate reflectance, ΔT_(m) representspropagating temperature increase, from ambient, required for maintainingcreep flow (e.g., ΔT_(m)=T_(strain)−T_(ambient)), ρ represents substratedensity, λ represents substrate thermal conductivity, I₀ representslaser irradiance (W/m²), and t represents time.

Power dependence is illustrated in FIG. 30 whereby it can be observedthat simply increasing laser power during welding can induce greaterstress beyond the interface region with excess energy resulting in alarger stress. FIG. 30 is a plot providing stress location from anexemplary weld line. With reference to FIG. 30, stress location from anexemplary weld line can be determined using Equation (6) where theparameters employed were similar to those used previously:wavelength=355 nm, beam waist=500 μm, repetition rate=30,000 Hz, pulsewidth=10 ns, v_(s)=2 mm/sec, dwell time=0.25 second, Eagle XG®thickness=0.7 mm, and Tstrain=669° C. FIG. 30 and Equation (6) alsoprovide insight into why higher strain point glass substrates can resultin higher stress profiles. For example, the stress profile location Zscales as the square root of the ΔT_(m) term which is linearly relatedto T_(strain). Other attempts to predict experimental observations fromthese expressions can be limited not only by the assumptions used butalso by the information that can be calculated, e.g., where higher CTEmaterials are laser welded. Here it was discovered that low CTE glasssubstrates (less than about 5 ppm/° C.) were more easily welded thanhigher CTE glasses such as soda-lime glasses. These low CTE substratesincluded quartz, fused silica, Eagle XG®, Willow, and Lotus glasssubstrates. After significant experimentation, suitable conditions werediscovered making high quality welds in higher CTE glasses possible. Forexample, it was discovered that embodiments described herein can be usedto weld soda lime glass (CTEs of about 9 ppm/° C. or greater) using 1 μmLMG films without any pre-heating requirement of the substrates, muchless to the strain or annealing point. FIG. 31 is a series ofphotographs of laser welded soda lime glass according to someembodiments. With reference to FIG. 31, a high quality bond formationwas achieved using very low laser power and a nanosecond pulse-width UV(355 nm) laser. The laser weld conditions used for these non-limitingand illustrated welds included a pulse width=1 ns, repetition rate=5MHz, power=1 Watt, an approximately 20 μm beam spot resulting in 67 μmweld line, and v_(s)=50 mm/s. With continued reference to FIG. 31, apulsed, 355-nm laser was used to weld two 0.7 mm thick soda lime glassplates compressed together with one substrate having a sputtered 1 μmthick low melting glass film. The aforementioned example and experimentshould not limit the scope of the claims appended herewith as ranges of2 MHz and 5 MHz laser repetition rates with 1 ns pulse widths wereexplored at laser beam translation rates from 50 mm/s-400 mm/sec.Further, laser beam spots of approximately 20 μm-70 μm at the lowmelting glass film interface were also explored for exemplary welds. Insome embodiments, an exemplary weld line quality can be observed with afocal spot size of about 20 μm and a 50 mm/s translation rate. Therobustness of these welded substrates was also noted after subjectingthem to 100° C. for 4 hours without any crack formation.

FIG. 32 is a schematic illustration of some embodiments. With referenceto FIG. 32, an exemplary, non-limiting process of achieving laserwelding with absorbing thin films is illustrated where laser-thermalenergy can be delivered into a substrate/substrate interface 40 toobtain a diffusion bond relative contact area, as close to unity, in apredetermined time, while minimizing any collateral damage, e.g.,spatial extent and magnitude of tensile stress residue. This process canbe more pronounced for higher CTE substrates where the weld-interfaceformation rate is faster than the creation of the CTE-mismatch stressinterface. Thus, in some embodiments, a focused beam can be used at theweld interface along with higher velocity sweep rates to achieve anexemplary weld without any crack formation.

In some embodiments, laser welds can be achieved using a film thatabsorbs at an incident laser wavelength λ, preferably A %>about 20%. Inother embodiments, both the substrate and film can exhibit color centerformation at λ. In additional embodiments, a temperature effect can beemployed to increase absorption for either or both the film andsubstrate at λ. Such an exemplary temperature effect can also contributeto the improvement of seal or weld speed and can lower the heat affectedzone (HAZ) and can lower activation energy for creep flow, e.g., formsan eutectic system, an alloy, etc. In some embodiments, if transparencyis required, then a band gap may be provided in UV, or high absorptionin NIR, IR. Additional embodiments can provide a weld having aninterfacial surface energy γ_(weld-interface)>>residual γ_(stress field)and/or a total integrated bond strength∫∫γ_(weld-interface)∂A>>∫∫γ_(stress-field)∂A. Further embodiments caninclude a low laser intensity requirement whereby the laser peak photonflux is less than about 10²⁵ photons/sec/cm² and does not includemultiphoton behavior, ablation, or plasma generation.

While some embodiments have been described as utilizing low meltingglass or inorganic films, the claims appended herewith should not be solimited as embodiments can use UV absorbing films, IRA films, and/orother inorganic films situated between two substrates. As noted above,in some embodiments, color center formation in an exemplary substrateglass is not necessary and is a function of the UV absorption of thefilm, e.g., less than about 20%. It follows that, in other embodiments,if the UV absorption of the film is greater than about 20%, alternativesubstrates such as quartz, low CTE substrates, and the like, can readilyform welds. Furthermore, when high CTE substrates are used, thesesubstrates can be readily welded with exemplary high repetition ratelasers (e.g., greater than about 300 kHz to about 5 MHz) and/or a lowpeak power. Furthermore, in embodiments where absorption of the film isa contributing factor, IR absorbing (visible transparent films) can bewelded with the use of an exemplary IR laser system.

In various embodiments of the present disclosure, the glass sealingmaterials and resulting layers can be transparent and/or translucent,thin, impermeable, “green,” and configured to form hermetic seals at lowtemperatures and with sufficient seal strength to accommodate largedifferences in CTE between the sealing material and the adjacentsubstrates. In some embodiments, the sealing layers can be free offillers and/or binders. The inorganic materials used to form the sealinglayer(s) can be non-frit-based or powders formed from ground glasses insome embodiments (e.g., UVA, LMG, etc.). In other embodiments, thesealing layer material is a low T_(g) glass that has a substantialoptical absorption cross-section at a predetermined wavelength whichmatches or substantially matches the operating wavelength of a laserused in the sealing process. In additional embodiments, absorption atroom temperature of a laser processing wavelength by the low T_(g) glasslayer is at least 15%.

In general, suitable sealant materials include low T_(g) glasses andsuitably reactive oxides of copper or tin. The glass sealing materialcan be formed from low T_(g) materials such as phosphate glasses, borateglasses, tellurite glasses and chalcogenide glasses. As defined herein,a low T_(g) glass material has a glass transition temperature of lessthan 400° C., e.g., less than 350, 300, 250 or 200° C. Exemplary borateand phosphate glasses include tin phosphates, tin fluorophosphates andtin fluoroborates. Sputtering targets can include such glass materialsor, alternatively, precursors thereof. Exemplary copper and tin oxidesare CuO and SnO, which can be formed from sputtering targets comprisingpressed powders of these materials. Optionally, the glass sealingcompositions can include one or more dopants, including but not limitedto tungsten, cerium and niobium. Such dopants, if included, can affect,for example, the optical properties of the glass layer, and can be usedto control the absorption by the glass layer of laser radiation. Forinstance, doping with ceria can increase the absorption by a low T_(g)glass barrier at laser processing wavelengths. Additional suitablesealant materials include laser absorbing low liquidus temperature (LLT)materials with a liquidus temperature less than or equal to about 1000°C., less than or equal to about 600° C., or less than or equal to about400° C. In other embodiments, the composition of the inorganic film canbe selected to lower the activation energy for inducing creep flow ofthe first substrate, the second substrate, or both the first and secondsubstrates as described above.

Exemplary tin fluorophosphate glass compositions can be expressed interms of the respective compositions of SnO, SnF₂ and P₂O₅ in acorresponding ternary phase diagram. Suitable UVA glass films caninclude SnO₂, ZnO, TiO₂, ITO, and other low melting glass compositions.Suitable tin fluorophosphates glasses include 20-100 mol % SnO, 0-50 mol% SnF₂ and 0-30 mol % P₂O₅. These tin fluorophosphates glasscompositions can optionally include 0-10 mol % WO₃, 0-10 mol % CeO₂and/or 0-5 mol % Nb₂O₅. For example, a composition of a doped tinfluorophosphate starting material suitable for forming a glass sealinglayer comprises 35 to 50 mole percent SnO, 30 to 40 mole percent SnF₂,15 to 25 mole percent P₂O₅, and 1.5 to 3 mole percent of a dopant oxidesuch as WO₃, CeO₂ and/or Nb₂O₅. A tin fluorophosphate glass compositionaccording to one particular embodiment can be a niobium-doped tinoxide/tin fluorophosphate/phosphorus pentoxide glass comprising about38.7 mol % SnO, 39.6 mol % SnF₂, 19.9 mol % P₂O₅ and 1.8 mol % Nb₂O₅.Sputtering targets that can be used to form such a glass layer mayinclude, expressed in terms of atomic mole percent, 23.04% Sn, 15.36% F,12.16% P, 48.38% O and 1.06% Nb.

A tin phosphate glass composition according to another embodimentcomprises about 27% Sn, 13% P and 60% O, which can be derived from asputtering target comprising, in atomic mole percent, about 27% Sn, 13%P and 60% O. As will be appreciated, the various glass compositionsdisclosed herein may refer to the composition of the deposited layer orto the composition of the source sputtering target. As with the tinfluorophosphates glass compositions, example tin fluoroborate glasscompositions can be expressed in terms of the respective ternary phasediagram compositions of SnO, SnF₂ and B₂O₃. Suitable tin fluoroborateglass compositions include 20-100 mol % SnO, 0-50 mol % SnF₂ and 0-30mol % B₂O₃. These tin fluoroborate glass compositions can optionallyinclude 0-10 mol % WO₃, 0-10 mol % CeO₂ and/or 0-5 mol % Nb₂O₅.Additional aspects of suitable low T_(g) glass compositions and methodsused to form glass sealing layers from these materials are disclosed incommonly-assigned U.S. Pat. No. 5,089,446 and U.S. patent applicationSer. Nos. 11/207,691, 11/544,262, 11/820,855, 12/072,784, 12/362,063,12/763,541, 12/879,578, and 13/841,391 the entire contents of which areincorporated by reference herein.

Exemplary substrates (glass or otherwise) can have any suitabledimensions. Substrates can have areal (length and width) dimensions thatindependently range from 1 cm to 5 m (e.g., 0.1, 1, 2, 3, 4 or 5 m) anda thickness dimension that can range from about 0.5 mm to 2 mm (e.g.,0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.5 or 2 mm). In further embodiments,a substrate thickness can range from about 0.05 mm to 0.5 mm (e.g.,0.05, 0.1, 0.2, 0.3, 0.4 or 0.5 mm). In still further embodiments, aglass substrate thickness can range from about 2 mm to 10 mm (e.g., 2,3, 4, 5, 6, 7, 8, 9 or 10 mm). A total thickness of an exemplary glasssealing layer can range from about 100 nm to 10 microns. In variousembodiments, a thickness of the layer can be less than 10 microns, e.g.,less than 10, 5, 2, 1, 0.5 or 0.2 microns. Exemplary glass sealing layerthicknesses include 0.1, 0.2, 0.5, 1, 2, 5 or 10 microns. The width ofthe sealed region, which can be proportional to the laser spot size, canbe about 0.05 to 2 mm, e.g., 0.05, 0.1, 0.2, 0.5, 1, 1.5 or 2 mm. Atranslation rate of the laser (i.e., sealing rate) can range from about1 mm/sec to 1000 mm/sec, such as 1, 2, 5, 10, 20, 50, 100, 200, 400, or1000 mm/sec. The laser spot size (diameter) can be about 0.02 to 1 mm.

Thus, it has been discovered that suitable laser welding glass substrateinterfaces can occur in embodiments of the present disclosure when thelocal glass temperature exceeds its strain or annealing temperature(e.g., 669° C. and 772° C. respectively for EXG) within a spatialextent, e.g., the “welding volume”. This volume can be dependent uponthe incident laser power, the composition of the UVA or LMG melt, andcolor center formation (as a result of impurities in the respectivesubstrates). Once attained, the volume can be swept over the interfacialregions to result in a rapid and strong seal between two substrates(glass or otherwise). Sealing speeds in excess of 5-1000 mm/s can beattained. Exemplary laser welds can experience an abrupt transition torelatively cold ambient temperatures from the high temperaturesassociated with the melt volume as it is swept away over the substrateregions of interest. The integrity of the hermetic seal and itsrespective strength can be maintained by slow cooling (self-annealing)of the hot base glass color center (relaxation) regions and the thinnessof the UVA or LMG or NIR thin film region (typically ½-1 μm) therebynullifying any impact of CTE mismatching between the two respectivesubstrates (glass or otherwise).

According to embodiments, the choice of the sealing layer material andthe processing conditions for forming a sealing layer over a glasssubstrate are sufficiently flexible that the substrate is not adverselyaffected by formation of the glass layer. Low melting temperatureglasses can be used to seal or bond different types of substrates.Sealable and/or bondable substrates include glasses, glass-glasslaminates, glass-polymer laminates, glass-ceramics or ceramics,including gallium nitride, quartz, silica, calcium fluoride, magnesiumfluoride or sapphire substrates. Additional substrates can be, but arenot limited to, metal substrates including tungsten, molybdenum, copper,or other types of suitable metal substrates. In some embodiments, onesubstrate can be a phosphor-containing glass plate, which can be used,for example, in the assembly of a light emitting device. Aphosphor-containing glass plate, for example, comprising one or more ofa metal sulfide, metal silicate, metal aluminate or other suitablephosphor, can be used as a wavelength-conversion plate in white LEDlamps. White LED lamps typically include a blue LED chip that is formedusing a group III nitride-based compound semiconductor for emitting bluelight. White LED lamps can be used in lighting systems, or as backlightsfor liquid crystal displays, for example. The low melting temperatureglasses and associate sealing method disclosed herein can be used toseal or encapsulate the LED chip.

Exemplary processes according to embodiments of the present disclosurecan be made possible because of the base substrate (glass or otherwise)properties due to the ability of the substrate to form color centerswith the prevailing laser illumination conditions and resultingtemperature enhancement. In some embodiments, the color center formationcan be reversible if transparent seals are desired. If the substrateshave dissimilar thicknesses, then thermally conductive substrates can beemployed in some embodiments to restore weld integrity.

Exemplary embodiments can thus utilize low melting temperature materialsto laser-weld glass or other material substrates together with a lowlaser pulse peak-power to minimize creation of shock waves and to ensureno micro cracks appear which could compromise the tensile fracturestrength. Exemplary embodiments can also provide diffusion weldingwithout melt puddle propagation allowing an adequate lower temperaturesealing process. Due to the thinness of the film region, embodiments ofthe present disclosure can nullify any impact of CTE mismatching betweenthe two respective substrates and can be utilized to provide welding ofsimilarly or dissimilarly dimensioned substrates. Further, inembodiments of the present disclosure no patterning of film is requiredfor sealing as occurs in the case of frit or staining materials, andmanufacturers therefore do not have to reveal their proprietary designs.

The present disclosure also teaches how low melting temperaturematerials can be used to laser weld glass packages together enablinglong lived hermetic operation of passive and active devices sensitive todegradation by attack of oxygen and moisture. As noted above,embodiments described herein provide UVA, LMG or other seals that can bethermally activated after assembly of the bonding surfaces using laserabsorption and can enjoy a higher manufacturing efficiency since therate of sealing each working device can be determined by thermalactivation and bond formation, rather than the rate one encapsulates adevice by inline thin film deposition in a vacuum or inert gas assemblyline. This can enable large sheet multiple device sealing withsubsequent scoring into individual devices (singulation), and due tohigh mechanical integrity the yield from singulation can be high.

Embodiments of the present disclosure also provide a laser sealingprocess, e.g., laser welding, diffusing welding, etc., that relies uponcolor center formation within the glass substrates due to extrinsiccolor centers, e.g., impurities or dopants, or intrinsic color centersinherent to the glass, at an incident laser wavelength, combined withexemplary laser absorbing films. Some non-limiting examples of filmsinclude SnO₂, ZnO, TiO₂, ITO, and low melting glass films which can beemployed at the interface of the glass substrates. Welds using thesematerials can provide visible transmission with sufficient UV absorptionto initiate steady state gentle diffusion welding. These materials canalso provide transparent laser welds having localized sealingtemperatures suitable for diffusion welding. Such diffusion weldingresults in low power and temperature laser welding of the respectiveglass substrates and can produce superior transparent welds withefficient and fast welding speeds. Exemplary laser welding processesaccording to embodiments of the present disclosure can also rely uponphoto-induced absorption properties of glass beyond color centerformation to include temperature induced absorption.

Hermetic encapsulation of a workpiece using the disclosed materials andmethods can facilitate long-lived operation of devices otherwisesensitive to degradation by oxygen and/or moisture attack. Exampleworkpieces, devices or applications include flexible, rigid orsemi-rigid organic LEDs, OLED lighting, OLED televisions, photovoltaics,MEMs displays, electrochromic windows, fluorophores, alkali metalelectrodes, transparent conducting oxides, quantum dots, etc.

As used herein, a hermetic layer is a layer which, for practicalpurposes, is considered substantially airtight and substantiallyimpervious to moisture and/or oxygen. By way of example, the hermeticseal can be configured to limit the transpiration (diffusion) of oxygento less than about 10⁻² cm³/m²/day (e.g., less than about 10⁻³cm³/m²/day), and limit the transpiration (diffusion) of water to about10⁻² g/m²/day (e.g., less than about 10⁻³, 10⁻⁴, 10⁻⁵ or 10⁻⁶ g/m²/day).In embodiments, the hermetic seal substantially inhibits air and waterfrom contacting a protected workpiece.

In some embodiments, a method of bonding two substrates comprisesforming a first glass layer on a sealing surface of a first substrate,forming a second glass layer on a sealing surface of a second substrate,placing at least a portion of the first glass layer in physical contactwith at least a portion of the second glass layer, and heating the glasslayers to locally melt the glass layers and the sealing surfaces to forma glass-to-glass weld between the first and second substrates. In eachof the sealing architectures disclosed herein, sealing using a lowmelting temperature glass layer can be accomplished by the localheating, melting and then cooling of both the glass layer and the glasssubstrate material located proximate to the sealing interface.

It is thus an aspect of embodiments of the present disclosure to combinethe ease of forming hermetic seals associated with laser welding to alsoform hermetic packages of active OLED or other devices to enable theirwidespread fabrication. Such fabrication would require welding overinterfacial conductive films. Unlike the methods disclosed herein,conventional methods of laser sealing can sever such interfacialconducting leads would sever them especially if the interfacetemperature gets too high or there is deleterious laser radiationinteraction with the conducting lead material. Embodiments of thepresent disclosure, however, provide an enabling disclosure of devicestructures requiring electrical biasing for hermetic device operationusing interfacial low melting temperature glass material film.Embodiments of the present subject matter may thus provide a successfullaser-welding of glass sheets or other substrates having an interfacialconductive film without destruction thereto or loss in performance.

In some embodiments, a method of bonding a workpiece comprises formingan inorganic film over a surface of a first substrate, arranging aworkpiece to be protected between the first substrate and a secondsubstrate wherein the film is in contact with the second substrate, andbonding the workpiece between the first and second substrates by locallyheating the film with laser radiation having a predetermined wavelength.The inorganic film, the first substrate, or the second substrate can betransmissive at approximately 420 nm to approximately 750 nm. In anotherembodiment, each of the inorganic film, first substrate and secondsubstrate are transmissive at approximately 420 nm to approximately 750nm. In a further embodiment, absorption of the inorganic film is morethan 10% at a predetermined laser wavelength. In an additionalembodiment, the composition of the inorganic film can be, but is notlimited to, SnO₂, ZnO, TiO₂, ITO, Zn, Ti, Ce, Pb, Fe, Va, Cr, Mn, Mg,Ge, SnF₂, ZnF₂ and combinations thereof. In other embodiments, thecomposition of the inorganic film can be selected to lower theactivation energy for inducing creep flow of the first substrate, thesecond substrate, or both the first and second substrates. In anotherembodiment, the composition of the inorganic film can be a laserabsorbing low liquidus temperature material with a liquidus temperatureless than or equal to about 1000° C., less than or equal to about 600°C., or less than or equal to about 400° C. In further embodiments, thestep of bonding can create a bond having an integrated bond strengthgreater than an integrated bond strength of a residual stress field inthe first substrate, second substrate or both the first and secondsubstrates. In some exemplary embodiments, such a bond will fail only bycohesive failure. In a further embodiment, the composition of theinorganic film comprises 20-100 mol % SnO, 0-50 mol % SnF₂, and 0-30 mol% P₂O₅ or B₂O₃. In some embodiments, the inorganic film and the firstand second substrates have a combined internal transmission of more than80% at approximately 420 nm to approximately 750 nm. In otherembodiments, the step of bonding further comprises bonding the workpiecebetween the first and second substrates as a function of the compositionof impurities in the first or second substrates and as a function of thecomposition of the inorganic film though the local heating of theinorganic film with laser radiation having a predetermined wavelength.Exemplary impurities in the first or second substrates can be, but arenot limited to, As, Fe, Ga, K, Mn, Na, P, Sb, Ti, Zn, Sn andcombinations thereof. In further embodiments, the first and secondsubstrates have different lateral dimensions, different CTEs, differentthicknesses, or combinations thereof. In some embodiments, one of thefirst and second substrates can be glass or glass-ceramic. Of course,the other of the first and second substrates can be a glass-ceramic,ceramic or metal. In some embodiments, the method can also include thestep of annealing the bonded workpiece. In other embodiments, the laserradiation comprises UV radiation at a predetermined wavelength betweenapproximately 193 nm to approximately 420 nm, NIR radiation at apredetermined wavelength between approximately 780 nm to approximately5000 nm, can include a pulse-width from 1 to 40 nanoseconds and arepetition rate of at least 1 kHz, and/or can be continuous wave. Infurther embodiments, a thickness of the inorganic film ranges from about10 nm to 100 micrometers. In some embodiments, the first, second orfirst and second substrates can comprise an alkaline earthboro-aluminosilicate glass, thermally strengthened glass, chemicallystrengthened glass, boro-silicate glass, alkali-aluminosilicate glass,soda-lime glass, and combinations thereof. In other embodiments, themethod can include the step of moving a laser spot formed by the laserradiation at a speed of approximately 1 mm/s to approximately 1000 mm/sto create a minimal heating zone. This speed, in some embodiments, doesnot exceed the product of a diameter of the laser spot and a repetitionrate of the laser radiation. In further embodiments, the step of bondingcan create a bond line having a width of approximately 50 μm toapproximately 1000 μm. In other embodiments, the inorganic film, firstsubstrate, or second substrate can be optically transparent before andafter the step of bonding in a range of greater than 80%, between 80% to90%, greater than 85%, or greater than 90% at about 420 nm to about 750nm. An exemplary workpiece can be, but is not limited to, a lightemitting diode, an organic light emitting diode, a conductive lead, asemiconductor chip, an ITO lead, a patterned electrode, a continuouselectrode, quantum dot materials, phosphor, and combinations thereof.

In other embodiments, a bonded device is provided comprising aninorganic film formed over a surface of a first substrate, and a deviceprotected between the first substrate and a second substrate wherein theinorganic film is in contact with the second substrate. In such anembodiment, the device includes a bond formed between the first andsecond substrates as a function of the composition of impurities in thefirst or second substrates and as a function of the composition of theinorganic film though a local heating of the inorganic film with laserradiation having a predetermined wavelength. Further, the inorganicfilm, the first substrate, or the second substrate can be transmissiveat approximately 420 nm to approximately 750 nm. In another embodiment,each of the inorganic film, first substrate and second substrate aretransmissive at approximately 420 nm to approximately 750 nm. In afurther embodiment, absorption of the inorganic film is more than 10% ata predetermined laser wavelength. In an additional embodiment, thecomposition of the inorganic film can be, but is not limited to, SnO₂,ZnO, TiO₂, ITO, Zn, Ti, Ce, Pb, Fe, Va, Cr, Mn, Mg, Ge, SnF₂, ZnF₂ andcombinations thereof. In other embodiments, the composition of theinorganic film can be selected to lower the activation energy forinducing creep flow of the first substrate, the second substrate, orboth the first and second substrates. In another embodiment, thecomposition of the inorganic film can be a laser absorbing low liquidustemperature material with a liquidus temperature less than or equal toabout 1000° C., less than or equal to about 600° C., or less than orequal to about 400° C. In further embodiments, the bond can have anintegrated bond strength greater than an integrated bond strength of aresidual stress field in the first substrate, second substrate or boththe first and second substrates. In some exemplary embodiments, such abond will fail only by cohesive failure. In a further embodiment, thecomposition of the inorganic film comprises 20-100 mol % SnO, 0-50 mol %SnF₂, and 0-30 mol % P₂O₅ or B₂O₃. In some embodiments, the inorganicfilm and the first and second substrates have a combined internaltransmission of more than 80% at approximately 420 nm to approximately750 nm. Exemplary impurities in the first or second substrates can be,but are not limited to, As, Fe, Ga, K, Mn, Na, P, Sb, Ti, Zn, Sn andcombinations thereof. In further embodiments, the first and secondsubstrates have different lateral dimensions, different CTEs, differentthicknesses, or combinations thereof. In some embodiments, one of thefirst and second substrates can be glass or glass-ceramic. Of course,the other of the first and second substrates can be a glass-ceramic,ceramic or metal. In further embodiments, a thickness of the inorganicfilm ranges from about 10 nm to 100 micrometers. In some embodiments,the first, second or first and second substrates can comprise analkaline earth boro-aluminosilicate glass, alkali-aluminosilicate glass,thermally strengthened glass, chemically strengthened glass, soda-limeglass, boro-silicate glass and combinations thereof. In otherembodiments, the inorganic film, first substrate, or second substratecan be optically transparent before and after the step of bonding in arange of greater than 80%, between 80% to 90%, greater than 85%, orgreater than 90% at about 420 nm to about 750 nm. An exemplary devicecan be, but is not limited to, a light emitting diode, an organic lightemitting diode, a conductive lead, a semiconductor chip, an ITO lead, apatterned electrode, a continuous electrode, quantum dot materials,phosphor, and combinations thereof. In some embodiments, the bond can behermetic with a closed loop or with seal lines crossing at anglesgreater than about 1 degree, can include spatially separated bond spots,and/or can be located at less than about 1000 μm from heat sensitivematerial of the bond. In other embodiments, birefringence around thebond can be patterned.

In further embodiments, a method of protecting a device is providedcomprising forming an inorganic film layer over a first portion surfaceof a first substrate, arranging a device to be protected between thefirst substrate and a second substrate wherein the sealing layer is incontact with the second substrate, and locally heating the inorganicfilm layer and the first and second substrates with laser radiation tomelt the sealing layer and the substrates to form a seal between thesubstrates. The first substrate can be comprised of glass orglass-ceramics, and the second substrate can be comprised of metal,glass-ceramics or ceramic. In some embodiments, the first and secondsubstrates have different lateral dimensions, different CTEs, differentthicknesses, or combinations thereof. In other embodiments, the devicecan be, but is not limited to, an ITO lead, a patterned electrode, and acontinuous electrode. In some embodiments, the step of locally heatingfurther comprises adjusting power of the laser radiation to reducedamage to the formed seal. An exemplary film can be, but is not limitedto, a low T_(g) glass, which comprises 20-100 mol % SnO, 0-50 mol %SnF₂, and 0-30 mol % P₂O₅ or B₂O₃. In other embodiments, the compositionof the inorganic film can be selected to lower the activation energy forinducing creep flow of the first substrate, the second substrate, orboth the first and second substrates. In another embodiment, thecomposition of the inorganic film can be a laser absorbing low liquidustemperature material with a liquidus temperature less than or equal toabout 1000° C., less than or equal to about 600° C., or less than orequal to about 400° C. In further embodiments, the step of bonding cancreate a bond having an integrated bond strength greater than anintegrated bond strength of a residual stress field in the firstsubstrate, second substrate or both the first and second substrates. Insome exemplary embodiments, such a bond will fail only by cohesivefailure.

While this description can include many specifics, these should not beconstrued as limitations on the scope thereof, but rather asdescriptions of features that can be specific to particular embodiments.Certain features that have been heretofore described in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features can be described above as acting in certaincombinations and can even be initially claimed as such, one or morefeatures from a claimed combination can in some cases be excised fromthe combination, and the claimed combination can be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings or figures in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all illustrated operations be performed, to achievedesirable results. In certain circumstances, multitasking and parallelprocessing can be advantageous.

As shown by the various configurations and embodiments illustrated inFIGS. 1-34, various embodiments for laser sealing using low meltingglass or thin absorbing films have been described.

While preferred embodiments of the present disclosure have beendescribed, it is to be understood that the embodiments described areillustrative only and that the scope of the invention is to be definedsolely by the appended claims when accorded a full range of equivalence,many variations and modifications naturally occurring to those of skillin the art from a perusal hereof.

We claim:
 1. A bonding method comprising: forming an inorganic film overa surface of a first substrate; positioning a second substrate incontact with the inorganic film; and locally heating the inorganic filmwith laser radiation having a predetermined wavelength to form a weldregion comprising a bond between the first and second substrates andextending from a first depth in the first substrate to a second depth inthe second substrate, wherein the inorganic film comprises at least oneinorganic film element and wherein one or both of the first and secondsubstrates comprises at least one inorganic substrate element; andwherein a first inorganic film element concentration of the first orsecond substrate in the weld region is higher than a second inorganicfilm element concentration of the first or second substrate outside theweld region.
 2. The method of claim 1, further comprising arrangingworkpiece between the first and second substrates prior to locallyheating the inorganic film with laser radiation.
 3. The method of claim1, wherein the bond between the first and second substrates is formed asa function of the composition of impurities in the first or secondsubstrates and as a function of the composition of the inorganic filmthrough the local heating of the inorganic film with laser radiationhaving the predetermined wavelength.
 4. The method of claim 1, furthercomprising forming a second inorganic film over a surface of the secondsubstrate.
 5. The method of claim 1, wherein the at least one inorganicfilm element is chosen from F, P, Sn, B, Bi, Zn, Ti, W, Ce, Nb, Pb, Fe,Va, Cr, Mn, Mg, Ge, and combinations thereof.
 6. The method of claim 1,wherein the first inorganic film element concentration is at least about5 mol % higher than the second inorganic film element concentration. 7.The method of claim 1, wherein a first substrate element concentrationof the weld region is higher than a second substrate elementconcentration of the inorganic film outside the weld region.
 8. Themethod of claim 7, wherein the at least one inorganic substrate elementis chosen from Al, B, Si, Na, Li, K, Mg, Ca, Ba, and combinationsthereof.
 9. The method of claim 7, wherein the first substrate elementconcentration is at least about 30 mol % higher than the secondsubstrate element concentration.
 10. The method of claim 1, wherein theinorganic film has the following composition: 20-100 mol % SnO; 0-50 mol% SnF₂; and 0-30 mol % P₂O₅ or B₂O₃.
 11. The method of claim 1, whereinthe inorganic film has the following composition: 10-80 mol % B₂O₃; 5-60mol % Bi₂O₃; and 0-70 mol % ZnO.
 12. A bonding method comprising:forming an inorganic film over a surface of a first substrate;positioning a second substrate in contact with the inorganic film; andlocally heating the inorganic film with laser radiation having apredetermined wavelength to form a weld region comprising a bond betweenthe first and second substrates and extending from a first depth in thefirst substrate to a second depth in the second substrate, wherein theinorganic film comprises at least one inorganic film element and whereinone or both of the first and second substrates comprises at least oneinorganic substrate element; and wherein a first substrate elementconcentration of the weld region is higher than a second substrateelement concentration of the inorganic film outside the weld region. 13.The method of claim 12, further comprising arranging a workpiece betweenthe first and second substrates prior to locally heating the inorganicfilm with laser radiation.
 14. A bonding method comprising: forming aninorganic film over a surface of a first substrate; positioning a secondsubstrate in contact with the inorganic film; and locally heating theinorganic film with laser radiation having a predetermined wavelength toform a stress region comprising a bond between the first and secondsubstrates and extending from a first depth in the first substrate to asecond depth in the second substrate, wherein a first stress in thestress region is greater than a second stress outside of the stressregion.
 15. The method of claim 14, further comprising arrangingworkpiece between the first and second substrates prior to locallyheating the inorganic film with laser radiation.
 16. The method of claim14, wherein the bond between the first and second substrates is formedas a function of the composition of impurities in the first or secondsubstrates and as a function of the composition of the inorganic filmthrough the local heating of the inorganic film with laser radiationhaving the predetermined wavelength.
 17. The method of claim 14, furthercomprising forming a second inorganic film over a surface of the secondsubstrate.
 18. The method of claim 14, wherein the first stress rangesfrom greater than about 1 MPa to about 25 MPa.
 19. The method of claim14, wherein a ratio of the first stress to the second stress ranges fromabout 1.1:1 to about 25:1.
 20. The method of claim 14, wherein thestress region has a thickness ranging from about 20 microns to about 500microns.
 21. A sealed device comprising: an inorganic film formed over asurface of a first substrate; a second substrate in contact with theinorganic film; and a stress region comprising a bond formed between thefirst and second substrates and extending from a first depth in thefirst substrate to a second depth in the second substrate, wherein afirst stress in the stress region is greater than a second stressoutside of the stress region.
 22. The sealed device of claim 21, whereinthe inorganic film, and optionally at least one of the first or secondsubstrates is transmissive at wavelengths ranging from about 420 nm toabout 750 nm.
 23. The sealed device of claim 21, wherein at least one ofthe first or second substrates comprises a glass, glass-ceramic,ceramic, polymer, or metal.
 24. The sealed device of claim 21, furthercomprising a second inorganic film formed over a surface of the secondsubstrate.
 25. The sealed device of claim 21, wherein the inorganic filmhas a thickness ranging from about 0.1 microns to about 10 microns. 26.The sealed device of claim 21, wherein the inorganic film has thefollowing composition: 20-100 mol % SnO; 0-50 mol % SnF₂; and 0-30 mol %P₂O₅ or B₂O₃.
 27. The sealed device of claim 21, wherein the inorganicfilm has the following composition: 10-80 mol % B₂O₃; 5-60 mol % Bi₂O₃;and 0-70 mol % ZnO.
 28. The sealed device of claim 21, wherein thestress region has a thickness ranging from about 20 microns to about 500microns.
 29. The sealed device of claim 21, wherein the first stressranges from greater than about 1 MPa to about 25 MPa.
 30. The sealeddevice of claim 21, wherein a ratio of the first stress to the secondstress ranges from about 1.1:1 to about 25:1.